package utils;

/**
 * The Class Base64Processing is responsible for convert a byte array to a base64 format that could be sent
 * in XML messages and the backward conversion of him. Base64 is a method that makes correspond a character
 * between A-Z,a-z,1-9,+ and / to each 6 bytes of the byte array given. 
 */
public class Base64Processing {

	/**
	 * Given a byte array that method converts it to the base64 format.
	 * 
	 * @param src The byte array to be converted.
	 * 
	 * @return 	The String that contains the original byte array converted in base64.
	 */
	public static String  encodeData(byte[] src) {
		int aLen = src.length;
		int numFullGroups = aLen/3;
		int numBytesInPartialGroup = aLen - 3*numFullGroups;
		int resultLen = 4*((aLen + 2)/3);
		StringBuffer  result = new StringBuffer (resultLen);
		char[] intToAlpha = intToBase64;

		int inCursor = 0;
		for (int i=0; i<numFullGroups; i++) {
			int byte0 = src[inCursor++] & 0xff;
			int byte1 = src[inCursor++] & 0xff;
			int byte2 = src[inCursor++] & 0xff;
			result.append(intToAlpha[byte0 >> 2]);
			result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
			result.append(intToAlpha[(byte1 << 2)&0x3f | (byte2 >> 6)]);
			result.append(intToAlpha[byte2 & 0x3f]);
		}
		
		if (numBytesInPartialGroup != 0) {
			int byte0 = src[inCursor++] & 0xff;
			result.append(intToAlpha[byte0 >> 2]);
			if (numBytesInPartialGroup == 1) {
				result.append(intToAlpha[(byte0 << 4) & 0x3f]);
				result.append("==");
			} else {
				int byte1 = src[inCursor++] & 0xff;
				result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
				result.append(intToAlpha[(byte1 << 2)&0x3f]);
				result.append('=');
			}
		}
		return result.toString();
	}

	/**
	 * This array is a lookup table that translates 6-bit positive integer
	 * index values into their "Base64 Alphabet" equivalents as specified
	 * in Table 1 of RFC 2045.
	 */
	private static final char intToBase64[] = {
		'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
		'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
		'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
		'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
	};
	
	/**
	 * Given a String previously encoded in base64 decode it backward to byte array.
	 * 
	 * @param s the String that had been previously encoded in base64
	 * 
	 * @return 	The original byte array converted from base64.
	 */
	public static byte[] decodeData(String  s) {
		byte[] alphaToInt = base64ToInt;
		int sLen = s.length();
		int numGroups = sLen/4;
		if (4*numGroups != sLen)
			throw new IllegalArgumentException (
					"String length must be a multiple of four.");
		int missingBytesInLastGroup = 0;
		int numFullGroups = numGroups;
		if (sLen != 0) {
			if (s.charAt(sLen-1) == '=') {
				missingBytesInLastGroup++;
				numFullGroups--;
			}
			if (s.charAt(sLen-2) == '=')
				missingBytesInLastGroup++;
		}
		byte[] result = new byte[3*numGroups - missingBytesInLastGroup];

		int inCursor = 0, outCursor = 0;
		for (int i=0; i<numFullGroups; i++) {
			int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt);
			result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
			result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
			result[outCursor++] = (byte) ((ch2 << 6) | ch3);
		}

		if (missingBytesInLastGroup != 0) {
			int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
			result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));

			if (missingBytesInLastGroup == 1) {
				int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
				result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
			}
		}
		return result;
	}

	/**
	 * Translates the specified character, which is assumed to be in the
	 * "Base 64 Alphabet" into its equivalent 6-bit positive integer.
	 *
	 * @throw IllegalArgumentException or ArrayOutOfBoundsException if
	 * c is not in the Base64 Alphabet.
	 */
	private static int base64toInt(char c, byte[] alphaToInt) {
		int result = alphaToInt[c];
		if (result < 0)
			throw new IllegalArgumentException ("Illegal character " + c);
		return result;
	}

	/**
	 * This array is a lookup table that translates unicode characters
	 * drawn from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045)
	 * into their 6-bit positive integer equivalents. Characters that
	 * are not in the Base64 alphabet but fall within the bounds of the
	 * array are translated to -1.
	 */
	private static final byte base64ToInt[] = {
		-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
		-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
		-1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
		55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
		5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
		24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34,
		35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
	};
	
}


